Polarizing Plate Provided With Optical Compensation Layers and Image Display Apparatus Using the Same

ABSTRACT

To provide a polarizing plate provided with optical compensation layers capable of contributing to thickness reduction, preventing uneven display due to heat, and favorably preventing light leak in black display, and an image display apparatus using the same. The polarizing plate provided with optical compensation layers of the present invention includes a polarizer, a first optical compensation layer, a second optical compensation layer, and a third optical compensation layer in the stated order. The first optical compensation layer, the second optical compensation layer, and the third optical compensation layer each have predetermined absolute value of photoelastic coefficient, refractive index profile, and in-plane retardation and/or thickness direction retardation. An absorption axis of the polarizer and a slow axis of the first optical compensation layer form an angle of 10° to 30°. The absorption axis of the polarizer and a slow axis of the second optical compensation layer form an angle of 70° to 95°. The absorption axis of the polarizer and a slow axis of the third optical compensation layer form an angle of 70°to 95°.

TECHNICAL FIELD

The present invention relates to a polarizing plate provided withoptical compensation layers, and to an image display apparatus using thesame. In particular, the present invention relates to a polarizing plateprovided with optical compensation layers capable of contributing tothickness reduction, preventing uneven display due to heat, andfavorably preventing light leak in black display, and to an imagedisplay apparatus using the same.

BACKGROUND ART

There is proposed a semi-transmissive reflective liquid crystal displayapparatus as a liquid crystal display apparatus of VA mode, in additionto a transmissive liquid crystal display apparatus and a reflectiveliquid crystal display apparatus (see JP 11-242226 A and JP 2001-209065A, for example). The semi-transmissive reflective liquid crystal displayapparatus utilizes outside light in the same manner as in the reflectiveliquid crystal display apparatus in a bright place, and allowsvisualization of display with an internal light source such as backlightin a dark place. That is, the semi-transmissive reflective liquidcrystal display apparatus employs a display system combining reflectivemode and transmissive mode, and switches display mode to reflective modeor transmissive mode in accordance with brightness of its environment.As a result, the semi-transmissive reflective liquid crystal displayapparatus can provide a clear display even in a dark environment whilereducing power consumption, and thus is suitably used for a display partof a portable device.

A specific example of such a semi-transmissive reflective liquid crystaldisplay apparatus is a liquid crystal display apparatus including on aninner side of a lower substrate a reflective film which has a windowpart for light transmission formed on a metal film of aluminum or thelike and which serves as a semi-transmissive reflecting plate. In aliquid crystal display apparatus of reflective mode, outside lightentering from an upper substrate side passes through a liquid crystallayer, reflects on a reflective film on an inner side of the lowersubstrate, passes through the liquid crystal layer again, and exits fromthe upper substrate side, to thereby contribute in display. Meanwhile,in a liquid crystal display apparatus of transmissive mode, light frombacklight entering from the lower substrate side passes through thewindow part of the reflective film and through the liquid crystal layer,and exits from the upper substrate side, to thereby contribute indisplay. Thus, of a reflective film-formed region, a region having thewindow part formed becomes a transmissive display region, and theremaining region becomes a reflective display region.

However, in a conventional reflective or semi-transmissive liquidcrystal display apparatus of VA mode, problems of light leak in blackdisplay and reduction in contrast have not been solved for a long periodof time.

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

The present invention has been made in view of solving the conventionalproblems described above, and an object of the present invention istherefore to provide a polarizing plate provided with opticalcompensation layers capable of contributing to thickness reduction,preventing uneven display due to heat, and favorably preventing lightleak in black display, and an image display apparatus using the same.

Means for Solving the Problems

A polarizing plate provided with optical compensation layers accordingto an embodiment of the present invention includes a polarizer, a firstoptical compensation layer, a second optical compensation layer, and athird optical compensation layer in the stated order. The first opticalcompensation layer contains a resin having an absolute value ofphotoelastic coefficient of 2×10⁻¹¹ m²/N or less, and has a relationshipof nx>ny=nz and an in-plane retardation Re₁ of 200 to 300 nm; the secondoptical compensation layer contains a resin having an absolute value ofphotoelastic coefficient of 2×10⁻¹¹ m²/N or less, and has a relationshipof nx>ny=nz and an in-plane retardation Re₂ of 90 to 160 nm; and thethird optical compensation layer has a relationship of nx=ny>nz, anin-plane retardation Re₃ of 0 to 20 nm, and a thickness directionretardation Rth₃ of 30 to 300 nm. An absorption axis of the polarizerand a slow axis of the first optical compensation layer form an angle of10° to 30°; the absorption axis of the polarizer and a slow axis of thesecond optical compensation layer form an angle of 70° to 95°; and theabsorption axis of the polarizer and a slow axis of the third opticalcompensation layer form an angle of 70° to 95°.

In one embodiment of the invention, the third optical compensation layerhas a thickness of 1 to 50 μm.

In another embodiment of the invention, the third optical compensationlayer is formed of a cholesteric alignment fixed layer having aselective reflection wavelength region of 350 nm or less.

Alternatively, the third optical compensation layer includes a layerformed of a film having a relationship of nx=ny>nz and containing aresin having an absolute value of photoelastic coefficient of 2×10⁻¹m²/N or less and a cholesteric alignment fixed layer having a selectivereflection wavelength region of 350 nm or less.

According to another aspect of the invention, a liquid crystal panel isprovided. The liquid crystal panel includes the above-describedpolarizing plate provided with optical compensation layers, and a liquidcrystal cell.

In one embodiment of the invention, the liquid crystal cell is ofreflective or semi-transmissive VA mode.

According to still another aspect of the invention, a liquid crystaldisplay apparatus is provided. The liquid crystal display apparatusincludes the above-described liquid crystal panel.

According to still another aspect of the invention, an image displayapparatus is provided. The image display apparatus includes theabove-described polarizing plate provided with optical compensationlayers.

EFFECT OF THE INVENTION

As described above, according to the present invention, the angle formedbetween the absorption axis of the polarizer and the slow axis of eachof the first optical compensation layer (λ/2 plate), the second opticalcompensation layer (λ/4 plate), and the third optical compensation layer(negative C plate) is set within a predetermined range, to therebysignificantly improve light leak in black display in a reflective andsemi-transmissive liquid crystal display apparatus of VA mode, inparticular. The third optical compensation layer (negative C plate) isformed of a cholesteric alignment fixed layer by using a liquid crystalmaterial and a chiral agent, to thereby drastically reduce its thicknesscompared with that of a conventional negative C plate. As a result, thepresent invention may greatly contribute to reduction in thickness of animage display apparatus. Further, by reducing the thickness of the thirdoptical compensation layer (negative C plate), uneven display due toheat may be significantly prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A schematic sectional view of a polarizing plate provided withoptical compensation layers according to a preferred embodiment of thepresent invention.

FIG. 2 An exploded perspective view of a polarizing plate provided withoptical compensation layers according to a preferred embodiment of thepresent invention.

FIG. 3 A schematic sectional view of a liquid crystal display panel tobe used for a liquid crystal display apparatus according to a preferredembodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   10 polarizing plate provided with optical compensation layers-   11 polarizer-   12 first optical compensation layer-   13 second optical compensation layer-   14 third optical compensation layer-   20 liquid crystal cell-   100 liquid crystal panel

BEST MODE FOR CARRYING OUT THE INVENTION

(Definitions of Terms and Symbols)

Definitions of terms and symbols in the specification of the presentinvention are described below.

(1) The symbol “nx” refers to a refractive index in a directionproviding a maximum in-plane refractive index (that is, a slow axisdirection), and the symbol “ny” refers to a refractive index in adirection perpendicular to the slow axis in the same plane (that is, afast axis direction). The symbol “nz” refers to a refractive index in athickness direction. Further, the expression “nx=ny”, for example, notonly refers to the case where nx and ny are exactly equal but alsoincludes the case where nx and ny are substantially equal. In thespecification of the present invention, the phrase “substantially equal”includes the case where nx and ny differ within a range providing noeffects on overall polarization properties of a polarizing plateprovided with optical compensation layers in practical use.

(2) The term “in-plane retardation Re” refers to an in-plane retardationvalue of a film (layer) measured at 23° C. by using light of awavelength of 590 nm. Re can be determined from an equationRe=(nx−ny)×d, where nx and ny represent refractive indices of a film(layer) at a wavelength of 590 nm in a slow axis direction and a fastaxis direction, respectively, and d (nm) represents a thickness of thefilm (layer).

(3) The term “thickness direction retardation Rth” refers to a thicknessdirection retardation value measured at 23° C. by using light of awavelength of 590 nm. Rth can be determined from an equationRth=(nx−nz)×d, where nx and nz represent refractive indices of a film(layer) at a wavelength of 590 nm in a slow axis direction and athickness direction, respectively, and d (nm) represents a thickness ofthe film (layer).

(4) The subscript “1” attached to a term or symbol described in thespecification of the present invention represents a first opticalcompensation layer. The subscript “2” attached to a term or symboldescribed in the specification of the present invention represents asecond optical compensation layer. The subscript “3” attached to a termor symbol described in the specification of the present inventionrepresents a third optical compensation layer.

(5) The term “λ/2 plate” refers to a plate having a function ofconverting linearly polarized light having a specific vibrationdirection into linearly polarized light having a vibration directionperpendicular thereto, or converting right-handed circularly polarizedlight into left-handed circularly polarized light (or convertingleft-handed circularly polarized light into right-handed circularlypolarized light). The λ/2 plate has an in-plane retardation value of afilm (layer) of about ½ of a predetermined light wavelength (generally,visible light region).

(6) The term “λ/4 plate” refers to a plate having a function ofconverting linearly polarized light of a specific wavelength intocircularly polarized light (or converting circularly polarized lightinto linearly polarized light). The λ/4 plate has an in-planeretardation value of a film (layer) of about ¼ of a predetermined lightwavelength (generally, visible light region).

(7) The term “cholesteric alignment fixed layer” refers to a layer inwhich: molecules forming the layer form a helical structure; a helicalaxis of the helical structure is aligned substantially perpendicular toa plane direction; and an alignment state is fixed. Thus, the term“cholesteric alignment fixed layer” not only refers to the case whereliquid crystal compound exhibits a cholesteric liquid crystal phase, butalso includes the case where a non-liquid crystal compound has a pseudostructure of a cholesteric liquid crystal phase. For example, the“cholesteric alignment fixed layer” may be formed by: providing torsionto a liquid crystal material exhibiting a liquid crystal phase with achiral agent for alignment into a cholesteric structure (helicalstructure); subjecting the liquid crystal material to polymerizationtreatment or crosslinking treatment for fixing the alignment(cholesteric structure) of the liquid crystal material.

(8) The phrase “selective reflection wavelength region of 350 nm orless” indicates that a center wavelength λ of a selective reflectionwavelength region is 350 nm or less. For example, in the case where thecholesteric alignment fixed layer is formed by using a liquid crystalmonomer, the center wavelength λ of the selective reflection wavelengthregion may be represented by the following equation.λ=n×PIn the equation, n represents an average refractive index of the liquidcrystal monomer, and P represents a helical pitch (nm) of thecholesteric alignment fixed layer. The average refractive index n isrepresented by (n_(o)+n_(e))/2, and is generally within a range of 1.45to 1.65. n_(o) represents an ordinary refractive index of the liquidcrystal monomer, and n_(e) represents an extraordinary refractive indexof the liquid crystal monomer.

(9) The term “chiral agent” refers to a compound having a function ofaligning the liquid crystal material (nematic liquid crystals, forexample) into a cholesteric structure.

(10) The term “torsional force” refers to ability of the chiral agent toprovide torsion to the liquid crystal material and to align the liquidcrystal material into a cholesteric structure (helical structure). Ingeneral, the torsional force may be represented by the followingequation.Torsional force=1/(P×W)As described above, P represents a helical pitch (nm) of the cholestericalignment fixed layer. W represents a weight ratio of the chiral agent.The weight ratio W of the chiral agent may be represented by W=[X/(X+Y)]×100. X represents a weight of the chiral agent, and Y representsa weight of the liquid crystal material.A. Polarizing Plate Provided With Optical Compensation LayerA-1. Overall Structure of Polarizing Plate Provided With OpticalCompensation Layer

FIG. 1 is a schematic sectional view of a polarizing plate provided withoptical compensation layers according to a preferred embodiment of thepresent invention. FIG. 2 is an exploded perspective view explainingoptical axes of respective layers constituting the polarizing plateprovided with optical compensation layers. As shown in FIG. 1, apolarizing plate provided with optical compensation layers 10 includes apolarizer 11, a first optical compensation layer 12, a second opticalcompensation layer 13, and a third optical compensation layer 14 in thestated order. The layers of the polarizing plate provided with opticalcompensation layers are laminated through any appropriatepressure-sensitive adhesive layer or adhesive (not shown). For practicaluse, any appropriate protective film (not shown) may be laminated on thepolarizer 11 on a side having no optical compensation layer formed.Further, as required, a protective film may be provided between thepolarizer 11 and the first optical compensation layer 12.

The first optical compensation layer 12 contains a resin having anabsolute value of photoelastic coefficient of 2×10⁻¹¹ m²/N or less, andhas a relationship of nx>ny=nz and an in-plane retardation Re₁ of 200 to300 nm. The second optical compensation layer 13 contains a resin havingan absolute value of photoelastic coefficient of 2×10⁻¹¹ m²/N or less,and has a relationship of nx>ny=nz and an in-plane retardation Re₂ of 90to 160 nm. The third optical compensation layer 14 has a relationship ofnx=ny>nz, an in-plane retardation Re₃ of 0 to 20 nm, and a thicknessdirection retardation Rth₃ of 30 to 300 nm. Details of the first opticalcompensation layer, second optical compensation layer, and third opticalcompensation layer are described below in the sections A-2, A-3, andA-4, respectively.

In the present invention, as shown in FIG. 2, the first opticalcompensation layer 12 is laminated such that its slow axis B forms apredetermined angle α with an absorption axis A of the polarizer 11. Theangle α is 10° to 30°, preferably 12° to 27°, and more preferably 14° to25° in a counterclockwise direction with respect to the absorption axisA of the polarizer 11. The second optical compensation layer 13 islaminated such that its slow axis C forms a predetermined angle β withthe absorption axis A of the polarizer 11. The angle β is 70° to 95°,preferably 72° to 93°, and more preferably 74° to 92° in acounterclockwise direction with respect to the absorption axis A of thepolarizer 11. The third optical compensation layer 14 is laminated suchthat its slow axis D forms a predetermined angle γ with the absorptionaxis A of the polarizer 11. The angle γ is 70° to 95°, preferably 72° to93°, and more preferably 74° to 92° in a counterclockwise direction withrespect to the absorption axis A of the polarizer 11. Three specificoptical compensation layers may be laminated in such a specificpositional relationship, to thereby significantly prevent light leak inblack display of a liquid crystal display apparatus of VA mode(reflective or semi-transmissive VA mode, in particular).

A total thickness of the polarizing plate provided with opticalcompensation layers of the present invention is preferably 80 to 270 μm,more preferably 110 to 270 μm, and most preferably 140 to 270 μm.According to the present invention, the third optical compensation layer(negative C plate: described below) is formed of a compositioncontaining a liquid crystal monomer and a chiral agent, to therebysignificantly increase a difference between nx and nz (nx>>nz). As aresult, the third optical compensation layer may have a very smallthickness. For example, a conventional negative C plate produced throughbiaxial stretching has a thickness of 60 μm or more, but the thirdoptical compensation layer to be used in the present invention may havea thickness down to 2 μm. As a result, the polarizing plate providedwith optical compensation layers of the present invention may have avery small total thickness compared with that of a conventionalpolarizing plate provided with optical compensation layers having asimilar structure (that is, a four-layer structure). As a result, thepolarizing plate provided with optical compensation layers of thepresent invention may greatly contribute to reduction in thickness of animage display apparatus.

A-2. First Optical Compensation Layer

The first optical compensation layer 12 may serve as a λ/2 plate. Thefirst optical compensation layer serves as a λ/2 plate, to therebyappropriately adjust retardation of wavelength dispersion properties (inparticular, a wavelength range where the retardation departs from λ/4)of the second optical compensation layer serving as a λ/4 plate. Such afirst optical compensation layer has an in-plane retardation Re₁ of 200to 300 nm, preferably 220 to 280 nm, and more preferably 230 to 270 nm.The first optical compensation layer 12 has a refractive index profileof nx>ny=nz.

A thickness of the first optical compensation layer may be set such thatit serves as a λ/2 plate most appropriately. That is, the thicknessthereof is set to provide a desired in-plane retardation. To bespecific, the thickness of the first optical compensation layer ispreferably 37 to 53 μm, more preferably 40 to 50 μm, and most preferably43 to 47 μm.

The first optical compensation layer 12 contains a resin having anabsolute value of photoelastic coefficient of 2×10⁻¹¹ m²/N or less,preferably 2.0×10⁻¹³ to 1.0×10⁻¹¹ m²/N, and more preferably 1.0×10⁻¹² to1.0×10⁻¹¹ m²/N. An absolute value of photoelastic coefficient within theabove ranges hardly causes change in retardation due to shrinkage stressunder heating. Thus, the first optical compensation layer may be formedby using a resin having such an absolute value of photoelasticcoefficient, to thereby favorably prevent uneven display due to heat ofan image display apparatus to be obtained.

Typical examples of the resin capable of satisfying such a photoelasticcoefficient include a cyclic olefin-based resin and a cellulose-basedresin. The cyclic olefin-based resin is particularly preferred. Thecyclic olefin-based resin is a general term for a resin prepared throughpolymerization of a cyclic olefin as a monomer, and examples thereofinclude resins described in JP 1-240517 A, JP 3-14882 A, JP 3-122137 A,and the like. Specific examples thereof include: a ring opened(co)polymer of a cyclic olefin; an addition polymer of a cyclic olefin;a copolymer (typically, a random copolymer) of a cyclic olefin, and anα-olefin such as ethylene or propylene; their graft modified productseach modified with an unsaturated carboxylic acid or its derivative; andhydrides thereof. A specific example of the cyclic olefin includes anorbornene-based monomer.

Examples of the norbornene-based monomer include: norbornene, its alkylsubstitution and/or alkylidene substitution such as5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene,5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and their products eachsubstituted by a polar group such as halogen; dicyclopentadiene and2,3-dihydrodicyclopentadiene; dimethano octahydronaphtalene, its alkylsubstitution and/or alkylidene substitution, and their products eachsubstituted by a polar group such as halogen, for example,6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtale ne,6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalen e,6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaph talene,6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtale ne,6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalen e,6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtal ene, and6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene; and a trimer of cyclopentadiene and a tetramer ofcyclopentadiene, for example,4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene.

In the present invention, other ring-opening polymerizable cycloolefinscan be combined without impairing the purpose of the present invention.Specific example of such cycloolefin includes a compound having onereactive double-bond, for example, cyclopentene, cyclooctene, and5,6-dihydrodicyclopentadiene.

The cyclic olefin-based resin has a number average molecular weight (Mn)of preferably 25,000 to 200,000, more preferably 30,000 to 100,000, andmost preferably 40,000 to 80,000 measured through a gel permeationchromatography (GPC) method by using a toluene solvent. A number averagemolecular weight within the above ranges can provide a resin havingexcellent mechanical strength, and favorable solubility, formingproperty, and casting operability.

In the case where the cyclic olefin-based resin is prepared throughhydrogenation of a ring opened polymer of a norbornene-based monomer, ahydrogenation rate is preferably 90% or more, more preferably 95% ormore, and most preferably 99% or more. A hydrogenation rate within theabove ranges can provide excellent heat degradation resistance, lightdegradation resistance, and the like.

For the cyclic olefin-based resin, various products are commerciallyavailable. Specific examples of the resin include the trade names“ZEONEX” and “ZEONOR” each manufactured by ZEON CORPORATION, the tradename “Arton” manufactured by JSR Corporation, the trade name “TOPAS”manufactured by TICONA Corporation, and the trade name “APEL”manufactured by Mitsui Chemicals, Inc..

Any appropriate cellulose-based resin (typically an ester of celluloseand acid) may be employed as the cellulose-based resin. An ester ofcellulose and fatty acid is preferred. Specific examples of suchcellulose-based resin include cellulose triacetate (triacetylcellulose:TAC), cellulose diacetate, cellulose tripropionate, and cellulosedipropionate. Cellulose triacetate (triacetyl cellulose: TAC) isparticularly preferred because it has low birefringence and hightransmittance. In addition, many products of TAC are commerciallyavailable, and thus TAC has advantages of availability and cost.

Specific examples of commercially available products of TAC include thetrade names “UV-50”, “UV-80”, “SH-50”, “SH-80”, “TD-80U”, “TD-TAC”, and“UZ-TAC” each manufactured by Fuji Photo Film CO., LTD., the trade name“KC series” manufactured by Konica Minolta Corporation, and the tradename “Triacetyl Cellulose 80 μm series” manufactured by Lonza JapanCorporation. Of those, “TD-80U” is preferred because of excellenttransmittance and durability. In particular, “TD-80U” has excellentadaptability to a TFT-type liquid crystal display apparatus.

The first optical compensation layer 12 is preferably obtained bystretching a film formed of the cyclic olefin-based resin or thecellulose-based resin. Any appropriate forming method may be employed asa method of forming a film from the cyclic olefin-based resin or thecellulose-based resin. Specific examples thereof include a compressionmolding method, a transfer molding method, an injection molding method,an extrusion molding method, a blow molding method, a powder moldingmethod, an FRP molding method, and a casting method. The extrusionmolding method and the casting method are preferred because a film to beobtained may have enhanced smoothness and favorable optical uniformity.Forming conditions may appropriately be set in accordance with thecomposition or type of resin to be used, properties desired for thefirst optical compensation layer, and the like. Many film products ofthe cyclic olefin-based resin and the cellulose-based resin arecommercially available, and the commercially available films may besubjected to the stretching treatment.

A stretch ratio of the film may vary depending on the in-planeretardation value and thickness desired for the first opticalcompensation layer, the type of resin to be used, the thickness of thefilm to be used, the stretching temperature, and the like. To bespecific, the stretch ratio is preferably 1.75 to 2.05 times, morepreferably 1.80 to 2.00 times, and most preferably 1.85 to 1.95 times.Stretching at such a stretch ratio may provide a first opticalcompensation layer having an in-plane retardation which mayappropriately exhibit the effect of the present invention.

A stretching temperature of the film may vary depending on the in-planeretardation value and thickness desired for the first opticalcompensation layer, the type of resin to be used, the thickness of thefilm to be used, the stretch ratio, and the like. To be specific, thestretching temperature is preferably 130 to 150° C., more preferably 135to 145° C., and most preferably 137 to 143° C. Stretching at such astretching temperature may provide a first optical compensation layerhaving an in-plane retardation which may appropriately exhibit theeffect of the present invention.

Referring to FIG. 1, the first optical compensation layer 12 is arrangedbetween the polarizer 11 and the second optical compensation layer 13.Any appropriate method may be employed as a method of arranging thefirst optical compensation layer in accordance with the purpose.Typically, the first optical compensation layer 12 is provided with apressure-sensitive adhesive layer (not shown) on each side, and thefirst optical compensation layer 12 is bonded to the polarizer 11 andthe second optical compensation layer 13. A gap between the layers isfilled with the pressure-sensitive adhesive layer as described above, tothereby prevent shift in relationship among optical axes of therespective layers and abrasion among the layers causing damages when thefirst optical compensation layer is incorporated into an image displayapparatus. Furthermore, reflection at the interface between therespective layers may be reduced, to thereby provide an image displayapparatus having high contrast.

The thickness of the pressure-sensitive adhesive layer may appropriatelybe set in accordance with the intended use, adhesive strength, and thelike. To be specific, the pressure-sensitive adhesive layer has athickness of preferably 1 μm to 100 μm, more preferably 5 μm to 50 μm,and most preferably 10 μm to 30 μm.

Any appropriate pressure-sensitive adhesive may be employed as apressure-sensitive adhesive forming the pressure-sensitive adhesivelayer. Specific examples thereof include a solvent-typepressure-sensitive adhesive, a nonaqueous emulsion-typepressure-sensitive adhesive, an aqueous pressure-sensitive adhesive, anda hot-melt pressure-sensitive adhesive. A solvent-typepressure-sensitive adhesive containing an acrylic polymer as a basepolymer is preferably used for exhibiting appropriate pressure-sensitiveadhesive properties (wettability, cohesiveness, and adhesiveness) withrespect to the polarizer and the first optical compensation layer andproviding excellent optical transparency, weatherability, and heatresistance.

A-3. Second Optical Compensation Layer

The second optical compensation layer 13 may serve as a λ/4 plate.According to the present invention, wavelength dispersion properties ofthe second optical compensation layer serving as a λ/4 plate may becorrected with optical properties of the first optical compensationlayer serving as a λ/2 plate, to thereby exhibit a function ofcircularly polarized light in a broad wavelength range. Such a secondoptical compensation layer has an in-plane retardation Re₂ of 90 to 160nm, preferably 100 to 150 nm, and more preferably 110 to 140 nm. Thesecond optical compensation layer 13 has a refractive index profile ofnx>ny=nz.

A thickness of the second optical compensation layer may be set suchthat it serves as a λ/4 plate most appropriately. That is, the thicknessthereof is set to provide a desired in-plane retardation. To bespecific, the thickness of the second optical compensation layer ispreferably 42 to 58 μm, more preferably 45 to 55 μm, and most preferably48 to 52 μm.

The second optical compensation layer 13 contains a resin having anabsolute value of photoelastic coefficient of 2×10⁻¹¹ m²/N or less,preferably 2.0×10⁻¹³ to 1.0×10⁻¹¹ m²/N, and more preferably 1.0×10⁻¹² to1.0×10⁻¹¹ m²/N. An absolute value of photoelastic coefficient within theabove ranges hardly causes change in retardation due to shrinkage stressunder heating. Thus, the second optical compensation layer may be formedby using a resin having such an absolute value of photoelasticcoefficient, to thereby favorably prevent uneven display due to heat ofan image display apparatus to be obtained, in cooperation with theeffect of the first optical compensation layer.

Typical examples of the resin capable of satisfying such a photoelasticcoefficient include a cyclic olefin-based resin and a cellulose-basedresin. Details of the cyclic olefin-based resin and the cellulose-basedresin are as described in the above section A-2.

The in-plane retardation Re₂ of the second optical compensation layer 13may preferably be controlled by changing the stretch ratio andstretching temperature of the cyclic olefin-based resin film or thecellulose-based resin film described in the above section A-2. Thestretch ratio may vary depending on the in-plane retardation value andthickness desired for the second optical compensation layer, the type ofresin to be used, the thickness of the film to be used, the stretchingtemperature, and the like. To be specific, the stretch ratio ispreferably 1.17 to 1.47 times, more preferably 1.22 to 1.42 times, andmost preferably 1.27 to 1.37 times. Stretching at such a stretch ratiomay provide a second optical compensation layer having an in-planeretardation which may appropriately exhibit the effect of the presentinvention.

A stretching temperature may vary depending on the in-plane retardationvalue and thickness desired for the second optical compensation layer,the type of resin to be used, the thickness of the film to be used, thestretch ratio, and the like. To be specific, the stretching temperatureis preferably 130 to 150° C., more preferably 135 to 145° C., and mostpreferably 137 to 143° C. Stretching at such a stretching temperaturemay provide a second optical compensation layer having an in-planeretardation which may appropriately exhibit the effect of the presentinvention.

Referring to. FIG. 1, the second optical compensation layer 13 isarranged between the first optical compensation layer 12 and the thirdoptical compensation layer 14. Any appropriate method may be employed asa method of arranging the second optical compensation layer inaccordance with the purpose. Typically, the second optical compensationlayer 13 is provided with a pressure-sensitive adhesive layer (notshown) on its first optical compensation layer 12 side, and the firstoptical compensation layer 12 is attached thereto. Furthermore, thesecond optical compensation layer 13 is provided with an adhesive layer(not shown) on its third optical compensation layer 14 side, and thethird optical compensation layer 14 is attached thereto. In the casewhere the third optical compensation layer 14 has a laminate structure(cholesteric alignment fixed layer/plastic film layer), the secondoptical compensation layer 13 and the plastic film layer are attachedtogether through a pressure-sensitive adhesive layer, and thecholesteric alignment fixed layer and the plastic film layer areattached together through an adhesive layer. Details of thepressure-sensitive adhesive layer are as described in the above sectionA-2.

A typical example of an adhesive used for forming the adhesive layerincludes a curable adhesive. Typical examples of the curable adhesiveinclude: a photo-curable adhesive such as a UV-curable adhesive; amoisture-curable adhesive; and a heat-curable adhesive. A specificexample of the heat-curable adhesive includes a thermosettingresin-based adhesive formed of an epoxy resin, an isocyanate resin, apolyimide resin, or the like. A specific example of the moisture-curableadhesive includes an isocyanate resin-based moisture-curable adhesive.The moisture-curable adhesive (in particular, an isocyanate resin-basedmoisture-curable adhesive) is preferred. The moisture-curable adhesivecures through a reaction with moisture in air, water adsorbed on asurface of an adherend, an active hydrogen group of a hydroxyl group ora carboxyl group or the like, etc. Thus, the adhesive may be applied andthen cured naturally by leaving at stand, and has excellent operability.Further, the moisture-curable adhesive requires no heating for curing,and thus the third optical compensation layer is not heated duringlamination (bonding). As a result, no heat shrinkage occurs, and thusformation of cracks during lamination or the like may significantly beprevented even in the case where the third optical compensation layerhas a very small thickness as in the present invention. In addition, thecurable adhesive hardly stretches or shrinks under heating after curing.Thus, formation of cracks during lamination or the like maysignificantly be prevented even in the case where the third opticalcompensation layer has a very small thickness or where a polarizingplate to be obtained is used under high temperature conditions. Notethat the isocyanate resin-based adhesive is a general term for apolyisocyanate-based adhesive and a polyurethane resin adhesive.

For example, a commercially available adhesive may be used as thecurable adhesive, or various curable resins may be dissolved ordispersed in a solvent to prepare a curable resin adhesive solution (ordispersion). In the case where the solution (or dispersion) is prepared,a ratio of the curable resin in the solution is preferably 10 to 80 wt%, more preferably 20 to 65%, especially preferably 25 to 65 wt %, andmost preferably 30 to 50 wt % in solid content. Any appropriate solventmay be used as the solvent in accordance with the type of curable resin,and specific examples thereof include ethyl acetate, methyl ethylketone, methyl isobutyl ketone, toluene, and xylene. Such solvent may beused alone or in combination.

An application amount of the adhesive to the second optical compensationlayer may appropriately be set in accordance with the purpose. Forexample, the application amount is preferably 0.3 to 3 ml, morepreferably 0.5 to 2 ml, and most preferably 1 to 2 ml per area (cm²) ofthe second optical compensation layer. After the application, thesolvent in the adhesive is evaporated through natural drying or heatdrying as required. A thickness of the adhesive layer to be obtained ispreferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and mostpreferably 1 to 10 μm. A Microhardness of the adhesive layer ispreferably 0.1 to 0.5 GPa, more preferably 0.2 to 0.5 GPa, and mostpreferably 0.3 to 0.4 GPa. Correlation between Microhardness and Vickershardness is known, and thus the Microhardness may be converted intoVickers hardness. The Microhardness may be calculated from indentationdepth and indentation load by using a thin-film hardness meter (tradenames, MH4000 and MHA-400, for example) manufactured by NEC Corporation.

A-4. Third Optical Compensation Layer

A-4-1. Overall Structure of Third Optical Compensation Layer

The third optical compensation layer 14 has a relationship of nx=ny>nzand may serve as a so-called negative C plate. The third opticalcompensation layer has such a refractive index profile, to thereby allowfavorable birefringence compensation of a liquid crystal layer of aliquid crystal cell of VA mode. As a result, a liquid crystal displayapparatus having significantly improved viewing angle properties can beobtained. As described above, the expression “nx=ny” not only refers tothe case where nx and ny are exactly equal but also includes the casewhere nx and ny are substantially equal. Thus, the third opticalcompensation layer may have an in-plane retardation and may have a slowaxis. The third optical compensation layer which may serve as a negativeC plate in practical use has an in-plane retardation Re₃ of 0 to 20 nm,preferably 0 to 10 nm, and more preferably 0 to 5 nm.

The third optical compensation layer 14 has a thickness directionretardation Rth₃ of 30 to 300 nm, preferably 60 to 180 nm, morepreferably 80 to 150 nm, and most preferably 100 to 120 nm. Thethickness of the third optical compensation layer for providing such athickness direction retardation may vary depending on a material to beused and the like. For example, the third optical compensation layer hasa thickness of preferably 1 to 50 μm, more preferably 1 to 20 μm, andmost preferably 1 to 15 μm. In the case where the third opticalcompensation layer is formed of a cholesteric alignment fixed layerdescribed below alone, the third optical compensation layer has athickness of preferably 1 to 10 μm, more preferably 1 to 8 μm, and mostpreferably 1 to 5 μm. Such a thickness is smaller than the thickness (60μm or more, for example) of the negative C plate obtained throughbiaxial stretching, and may greatly contribute to reduction in thicknessof an image display apparatus. Further, the third optical compensationlayer may be formed to have a very small thickness, to therebysignificantly prevent uneven display due to heat. Such an opticalcompensation layer having a very small thickness is preferred from theviewpoints of preventing disturbance in cholesteric alignment orreduction in transmittance, selective reflection property, colorprotection, productivity, and the like. The third optical compensationlayer (negative C plate) of the present invention may be formed from anyappropriate material as long as the above-mentioned thickness andoptical properties can be obtained. Preferably, a negative C platehaving such a very small thickness is realized by forming cholestericalignment by using a liquid crystal material and fixing the cholestericalignment, that is, by using a cholesteric alignment fixed layer(details of a material used for forming the cholesteric alignment and amethod of fixing the cholesteric alignment are described below).

Preferably, the third optical compensation layer 14 is formed of acholesteric alignment fixed layer having a selective reflectionwavelength region of 350 nm or less. An upper limit of the selectivereflection wavelength region is more preferably 320 nm or less, and mostpreferably 300 nm or less. Meanwhile, a lower limit of the selectivereflection wavelength region is preferably 100 nm or more, and morepreferably 150 nm or more. In the case where the selective reflectionwavelength region is more than 350 nm, the selective reflectionwavelength region covers a visible light region and thus may cause aproblem such as coloring or decoloring. In the case where the selectivereflection wavelength region is less than 100 nm, amount of a chiralagent (described below) to be used increases excessively and thus atemperature during formation of an optical compensation layer must becontrolled very accurately. As a result, a polarizing plate may hardlybe produced.

A helical pitch in the cholesteric alignment fixed layer is preferably0.01 to 0.25 μm, more preferably 0.03 to 0.20 μm, and most preferably0.05 to 0.15 μm. A helical pitch of 0.01 μm or more provides sufficientalignment property, for example. A helical pitch of 0.25 μm or lessallows sufficient suppression of rotary polarization in a shorterwavelength side of visible light, to thereby sufficiently prevent lightleak and the like. The helical pitch maybe controlled by adjusting thetype (torsional force) and amount of the chiral agent as describedbelow. The helical pitch may be adjusted, to thereby control theselective reflection wavelength region within a desired range.

Alternatively, the third optical compensation layer 14 may have alaminate structure of the cholesteric alignment fixed layer and a layer(also referred to as a plastic film layer in the specification of thepresent invention) having a relationship of nx=ny>nz and containing aresin having an absolute value of photoelastic coefficient of 2×10⁻¹¹m²/N or less. Typical examples of a material capable of forming theplastic film layer (resin capable of satisfying such a photoelasticcoefficient) include a cyclic olefin-based resin and a cellulose-basedresin. Details of the cyclic olefin-based resin and the cellulose-basedresin are as described in the above section A-2. A cellulose-based resinfilm (typically, a TAC film) is a film having a relationship ofnx=ny>nz.

A-4-2. Liquid Crystal Composition Forming Third Optical CompensationLayer (Cholesteric Alignment Fixed Layer): Liquid Crystal Material

The third optical compensation layer (cholesteric alignment fixed layer)may be formed of a liquid crystal composition. Any appropriate liquidcrystal material may be used as a liquid crystal material to be includedin the composition. The liquid crystal material (nematic liquidcrystals) preferably has a liquid crystal phase of a nematic phase.Examples of such a liquid crystal material that may be used include aliquid crystal polymer and a liquid crystal monomer. The liquid crystalmaterial may exhibit liquid crystallinity through a lyotropic orthermotropic mechanism. Further, liquid crystals are preferably alignedin homogeneous alignment. A content of the liquid crystal material inthe liquid crystal composition is preferably 75 to 95 wt %, and morepreferably 80 to 90 wt %. In the case where the content of the liquidcrystal material is less than 75 wt %, the composition may notsufficiently exhibit a liquid crystal state and thus the cholestericalignment may not be formed sufficiently. In the case where the contentof the liquid crystal material is more than 95 wt %, a content of achiral agent may be reduced to prevent sufficient torsion to be providedand thus the cholesteric alignment may not be formed sufficiently.

The liquid crystal material is preferably a liquid crystal monomer(polymerizable monomer or cross linking monomer, for example) because analignment state of the liquid crystal monomer can be fixed bypolymerizing or crosslinking the liquid crystal monomer as describedbelow. The alignment state may be fixed by aligning the liquid crystalmonomer and then, for example, polymerizing or crosslinking the liquidcrystal monomers with each other. As a result, a polymer is formedthrough polymerization and a three-dimensional network structure isformed through crosslinking. The polymer and the three-dimensionalnetwork structure are non-liquid crystalline. Thus, the thus-formedthird optical compensation layer does not transfer into, for example, aliquid crystal phase, glass phase, or crystal phase due to temperaturechange unique to a liquid crystal compound. As a result, the thirdoptical compensation layer realizes an optical compensation layer havingvery excellent stability and not affected by the temperature change.

Any suitable liquid crystal monomers may be employed as the liquidcrystal monomer. For example, there are used polymerizable mesogeniccompounds and the like described in JP 2002-533742 A (WO 00/37585), EP358208 (U.S. Pat. No. 5,211,877), EP 66137 (U.S. Pat. No. 4,388,453),WO93/22397, EP 0261712, DE 19504224, DE 4408171, GB 2280445, and thelike. Specific examples of the polymerizable mesogenic compoundsinclude: LC242 (trade name) available from BASF Aktiengesellschaft; E7(trade name) available from Merck & Co., Inc.; and LC-Silicone-CC3767(trade name) available from Wacker-Chemie GmbH.

For example, a nematic liquid crystal monomer is preferred as the liquidcrystal monomer, and a specific example thereof includes a monomerrepresented by the below-indicated formula (1). The liquid crystalmonomer may be used alone or in combination of two or more thereof.

In the above formula (1), A¹ and A² each represent a polymerizablegroup, and may be the same or different from each other. One of A¹ andA² may represent hydrogen. Each X independently represents a singlebond, —O—, —S—, —C═N—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NR—, —NR—CO—, —NR—,—O—CO—NR—, —NR—CO—O—, —CH₂—O—, or —NR—CO—NR—. R represents H or an alkylgroup having 1 to 4 carbon atoms. M represents a mesogen group.

In the above formula (1), Xs may be the same or different from eachother, but are preferably the same.

Of monomers represented by the above formula (1), each A² is preferablyarranged in an ortho position with respect to A¹.

A¹ and A² are preferably each independently represented by thebelow-indicated formula (2), and A¹ and A² preferably represent the samegroup.Z-X-(Sp)   (2)

In the above formula (2), Z represents a crosslinkable group, and X isthe same as that defined in the above formula (1). Sp represents aspacer consisting of a substituted or unsubstituted linear or branchedalkyl group having 1 to 30 carbon atoms. n represents 0 or 1. A carbonchain in Sp may be interrupted by oxygen in an ether functional group,sulfur in a thioether functional group, a non-adjacent imino group, analkylimino group having 1 to 4 carbon atoms, or the like.

In the above formula (2), Z preferably represents any one of functionalgroups represented by the below-indicated formulae. In thebelow-indicated formulae, examples of R include a methyl group, an ethylgroup, an n-propyl group, an i-propyl group, an n-butyl group, ani-butyl group, and a t-butyl group.

In the above formula (2), Sp preferably represents any one of structuralunits represented by the below-indicated formulae. In thebelow-indicated formulae, m preferably represents 1 to 3, and ppreferably represents 1 to 12.

In the above formula (1), M is preferably represented by thebelow-indicated formula (3). In the below-indicated formula (3), X isthe same as that defined in the above formula (1). Q represents asubstituted or unsubstituted linear or branched alkylene group, or anaromatic hydrocarbon group, for example. Q may represent a substitutedor unsubstituted linear or branched alkylene group having 1 to 12 carbonatoms, for example.

In the case where Q represents an aromatic hydrocarbon group, Qpreferably represents any one of aromatic hydrocarbon groups representedby the below-indicated formulae or substituted analogues thereof.

The substituted analogues of the aromatic hydrocarbon groups representedby the above formulae may each have 1 to 4 substituents per aromaticring, or 1 to 2 substituents per aromatic ring or group. Thesubstituents may be the same or different from each other. Examples ofthe substituents include: an alkyl group having 1 to 4 carbon atoms; anitro group; a halogen group such as F, Cl, Br, or I; a phenyl group;and an alkoxy group having 1 to 4 carbon atoms.

Specific examples of the liquid crystal monomer include monomersrepresented by the following formulae (4) to (19).

A temperature range in which the liquid crystal monomer exhibitsliquid-crystallinity varies depending on the type of liquid crystalmonomer. More specifically, the temperature range is preferably 40 to120° C., more preferably 50 to 100° C., and most preferably 60 to 90° C.

A-4-3. Liquid Crystal Composition Forming Third Optical CompensationLayer (Cholesteric Alignment Fixed Layer): Chiral Agent

The liquid crystal composition capable of forming the third opticalcompensation layer (cholesteric alignment fixed layer) preferablycontains a chiral agent. A content of the chiral agent in the liquidcrystal composition is preferably 5 to 23 wt %, and more preferably 10to 20 wt %. In the case where the content of the chiral agent is lessthan 5 wt %, torsion cannot be sufficiently provided and thus thecholesteric alignment may not be formed sufficiently. As a result, aselective reflection wavelength region of the optical compensation layerto be obtained may be hardly controlled to a desired region (shorterwavelength side). In the case where the content of the chiral agent ismore than 23 wt %, the liquid crystal material exhibits a liquid crystalstate in a very narrow temperature range and a temperature duringformation of an optical compensation layer must be controlled veryaccurately. As a result, production of a polarizing plate may involvedifficulties. Such chiral agent may be used alone or in combination.

The chiral agent may employ any appropriate material capable of aligningthe liquid crystal material into a desired cholesteric structure. Forexample, such a chiral agent has a torsional force of preferably 1×10⁻⁶nm⁻¹·(wt %)⁻¹ or more, more preferably 1×10⁻⁵ nm⁻¹·(wt %)⁻¹ to 1×10⁻²nm⁻¹·(wt %)⁻¹, and most preferably 1×10⁻⁴ nm⁻¹·(wt %)⁻¹ to 1×10⁻³nm⁻¹·(wt %)⁻¹. A chiral agent having such a torsional force may be used,to thereby control a helical pitch of the cholesteric alignment fixedlayer within a desired range and control the selective reflectionwavelength region within a desired range. For example, in the case wherechiral agents of equal torsional force are used, a larger content of thechiral agent in the liquid crystal composition provides an opticalcompensation layer having a selective reflection wavelength region on ashorter wavelength side. For example, in the case where the content ofthe chiral agent in the liquid crystal composition is equal, a chiralagent having a larger torsional force provides an optical compensationlayer having a selective reflection wavelength region on a shorterwavelength side. A specific example thereof is described below. Forsetting the selective reflection wavelength region of the opticalcompensation layer to be formed within a range of 200 to 220 nm, aliquid crystal composition may contain 11 to 13 wt % of a chiral agenthaving a torsional force of 5×10⁻⁴ nm⁻¹ (wt %)⁻¹, for example. Forsetting the selective reflection wavelength region of the opticalcompensation layer to be formed within a range of 290 to 310 nm, aliquid crystal composition may contain 7 to 9 wt % of a chiral agenthaving a torsional force of 5×10⁻⁴ nm⁻¹·(wt %)⁻¹, for example.

The chiral agent is preferably a polymerizable chiral agent. Specificexamples of the polymerizable chiral agent include chiral compoundsrepresented by the following general formulae (20) to (23).(Z-X⁵)_(n)Ch   (20)(Z-X²-Sp-X⁵)_(n)Ch   (21)(P¹—X⁵)_(n)Ch   (22)(Z-X²-Sp-X³-M-X⁴)_(n)Ch   (23)

In the formulae (20) to (23), Z and Sp are the same as those defined forthe above formula (2). X², X³, and X⁴ each independently represent achemical single bond, —O—, —S—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NR—,—NR—CO—, —O—CO—NR—, —NR—CO—O—, or —NR—CO—NR—. R represents H or an alkylgroup having 1 to 4 carbon atoms. X⁵ represents a chemical single bond,—O—, —S—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NR—, —NR—CO—, —O—CO—NR—,—NR—CO—O—, —NR—CO—NR—, —CH₂O—, —O—CH₂—, —CH═N—, —N═CH—, or —N≡N—. Rrepresents H or an alkyl group having 1 to 4 carbon atoms as describedabove. M represents a mesogenic group as described above. P¹ representshydrogen, an alkyl group having 1 to 30 carbon atoms, an acyl grouphaving 1 to 30 carbon atoms, or a cycloalkyl group having 3 to 8 carbonatoms which is substituted by 1 to 3 alkyl groups having 1 to 6 carbonatoms. n represents an integer of 1 to 6. Ch represents a chiral groupwith a valence of n. In the formula (23), at least one of X³ and X⁴preferably represents —O—CO—O—, —O—CO—NR—, —NR—CO—O—, or —NR—CO—NR—. Inthe formula (22), in the case where P¹ represents an alkyl group, anacyl group, or a cycloalkyl group, its carbon chain maybe interrupted byoxygen of an ether functional group, sulfur of a thioether functionalgroup, a non-adjacent imino group, or an alkyl imino group having 1 to 4carbon atoms.

Examples of the chiral group represented by Ch include atomic groupsrepresented by the following formulae.

In the atomic groups described above, L represents an alkyl group having1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, ahalogen, COOR, OCOR, CONHR, or NHCOR. R represents an alkyl group having1 to 4 carbon atoms. Note that terminals of the atomic groupsrepresented in the above formulae each represent a bonding hand to anadjacent group.

Of the atomic groups, atomic groups represented by the followingformulae are particularly preferred.

In a preferred example of the chiral compound represented by the aboveformula (21) or (23): n represents 2; Z represents H₂C═CH—; and Chrepresents atomic groups represented by the following formulae.

Specific examples of the chiral compound include compounds representedby the following formulae (24) to (44). Note that those chiral compoundseach have a torsional force of 1×10⁻⁶ nm⁻¹·(wt %)⁻¹ or more.

In addition to the chiral compounds represented above, further examplesof the chiral compound include chiral compounds described inRE-A4342280, DE 19520660.6, and DE 19520704.1.

Note that any appropriate combination of the liquid crystal material andthe chiral agent may be employed in accordance with the purpose.Particularly typical examples of the combination include: a combinationof the liquid crystal monomer represented by the above formula (10)/thechiral agent represented by the above formula (38); and a combination ofthe liquid crystal monomer represented by the above formula (11)/thechiral agent represented by the above formula (39).

A-4-4. Liquid Crystal Composition Forming Third Optical CompensationLayer (Cholesteric Alignment Fixed Layer): Other Additives

The liquid crystal composition capable of forming the third opticalcompensation layer (cholesteric alignment fixed layer) preferablycontains at least one of a polymerization initiator and a crosslinkingagent (curing agent). The polymerization initiator and/or thecrosslinking agent (curing agent) is used, to thereby favorably fix thecholesteric structure (cholesteric alignment) of the liquid crystalmaterial formed in a liquid crystal state. Any appropriate substance maybe used for the polymerization initiator or the crosslinking agent aslong as the effect of the present invention can be obtained. Examples ofthe polymerization initiator include benzoylperoxide (BPO) andazobisisobutyronitrile (AIBN). Examples of the crosslinking agent(curing agent) include a UV-curing agent, a photo-curing agent, and aheat-curing agent. Specific examples thereof include an isocyanate-basedcrosslinking agent, an epoxy-based crosslinking agent, and a metalchelate crosslinking agent. Such polymerization initiator orcrosslinking agent may be used alone or in combination. A content of thepolymerization initiator or the crosslinking agent in the liquid crystalcomposition is preferably 0.1 to 10 wt %, more preferably 0.5 to 8 wt %,and most preferably 1 to 5 wt %. In the case where the content of thepolymerization initiator or the crosslinking agent is less than 0.1 wt%, the cholesteric structure may be fixed insufficiently. In the casewhere the content of the polymerization initiator or the crosslinkingagent is more than 10 wt %, the liquid crystal material exhibits aliquid crystal state in a very narrow temperature range and temperaturecontrol during formation of an optical compensation layer may involvedifficulties.

The liquid crystal composition may further contain any appropriateadditive, as required. Examples of the additive include an antioxidant,modifier, surfactant, dye, pigment, discoloration inhibitor, andultraviolet absorber. Those additives may be used alone or incombination. More specifically, examples of the antioxidant include aphenol-based compound, an amine-based compound, an organic sulfur-basedcompound, and a phosphine-based compound. Examples of the modifierinclude glycols, silicones, and alcohols. The surfactant is added, forexample, in order to make the surface of an optical compensation layersmooth. Examples of the surfactant that can be used include asilicone-based surfactant, an acrylic surfactant, and a fluorine-basedsurfactant, and a silicone-based surfactant is particularly preferred.

A-4-5. Method of Forming Third Optical Compensation Layer (CholestericAlignment Fixed Layer)

Any appropriate method may be employed for the method of forming thethird optical compensation layer (cholesteric alignment fixed layer) aslong as the desired cholesteric alignment fixed layer can be obtained. Atypical method of forming the third optical compensation layer(cholesteric alignment fixed layer) involves: spreading the liquidcrystal composition on a substrate to form a spread layer; subjectingthe spread layer to heat treatment such that the liquid crystal materialin the liquid crystal composition is aligned in cholesteric alignment;subjecting the spread layer to at least one of polymerization treatmentand crosslinking treatment to fix the alignment of the liquid crystalmaterial; and transferring the cholesteric alignment fixed layer formedon the substrate. Hereinafter, a specific procedure for the method offorming the third optical compensation layer is described.

First, a liquid crystal material, a chiral agent, a polymerizationinitiator or a crosslinking agent, and various additives as required aredissolved or dispersed into a solvent to prepare a liquid crystalapplication liquid. The liquid crystal material, the chiral agent, thepolymerization initiator, the crosslinking agent, and the additive areas described above. A solvent to be used in the liquid crystalapplication liquid is not particularly limited. Specific example thereofincludes: halogenated hydrocarbons such as chloroform, dichloromethane,carbon tetrachloride, dichloroethane, tetrachloroethane, methylenechloride, trichloroethylene, tetrachloroethylene, chlorobenzene, andorthodichlorobenzene; phenols such as phenol, p-chlorophenol,o-chlorophenol, m-cresol, o-cresol, and p-cresol; aromatic hydrocarbonssuch as benzene, toluene, xylene, methoxybenzene, and1,2-dimethoxybenzene; ketone-based solvents such as acetone,methylethylketone (MEK), methylisobutylketone, cyclohexanone,cyclopentanone, 2-pyrolidone, and N-methyl-2-pyrolidone; ester-basedsolvents such as ethyl acetate and butyl acetate; alcohol-based solventssuch as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol,ethylene glycol monomethylether, diethylene glycol dimethylether,propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol;amide-based solvents such as dimethylformamide and dimethylacetoamide;nitrile-based solvents such as acetonitrile and butyronitrile;ether-based solvents such as diethylether, dibutylether, tetrahydroflan,and dioxane; carbon disufide; ethyl cellosolve; and butyl cellosolve. Ofthose, toluene, xylene, mesitylene, MEK, methyl isobutylketone,cyclohexanone, ethyl cellosolve, butyl cellosolve, ethyl acetate, butylacetate, propyl acetate, and ethyl cellosolve acetate are preferred.Those solvents may be used alone or in combination.

A viscosity of the liquid crystal application liquid may vary dependingon the content of the liquid crystal material or temperature. Forexample, in the case where a concentration of the liquid crystalmaterial in the liquid crystal application liquid is 5 to 70 wt % atabout room temperature (20 to 30° C.), the viscosity of the applicationliquid is preferably 0.2 to 20 mPa·s, more preferably 0.5to 15 mPa·s,and most preferably 1 to 10 mPa·s. To be more specific, in the casewhere the concentration of the liquid crystal material in the liquidcrystal application liquid is 30 wt %, the viscosity of the applicationliquid is preferably 2 to 5 mPa·s, and more preferably 3 to 4 mPa·s. Theapplication liquid having a viscosity of 0.2 mPa·s or more can favorablyprevent generation of liquid drip due to spreading of the applicationliquid. Further, the application liquid having a viscosity of 20 mPa·sor less can provide an optical compensation layer having very excellentsurface smoothness without uneven thickness and excellent applicationproperty.

Next, the liquid crystal application liquid is applied onto thesubstrate to form a spread layer. The method of forming the spread layermay employ any appropriate method (typically, method of fluid spreadingthe application liquid). Specific examples thereof include a rollcoating method, a spin coating method, a wire bar coating method, a dipcoating method, an extrusion coating method, a curtain coating method,and a spray coating method. Of those, the spin coating method and theextrusion coating method are preferred from the viewpoint of coatingefficiency.

An application amount of the liquid crystal application liquid mayappropriately be set in accordance with the concentration of theapplication liquid, the thickness of the intended layer, and the like.For example, in the case where the concentration of the liquid crystalmaterial in the application liquid is 20 wt %, the application amount ispreferably 0.03 to 0.17 ml, more preferably 0.05 to 0.15 ml, and mostpreferably 0.08 to 0.12 ml per area (100 cm²) of the substrate.

Any appropriate substrate capable of aligning the liquid crystalmaterial may be used as the substrate. Typically, the substrate includesvarious plastic films. Specific examples of the plastic includecellulose-based plastics such as triacetyl cellulose (TAC), polyolefinsuch as polyethylene, polypropylene or poly(4-methylpentene-1),polyimide, polyamideimide, polyether imide, polyamide,polyetheretherketone, polyetherketone, polyketone sulfide,polyethersulfone, polysulfone, polyphenylene sulfide, polyphenyleneoxide, polyethylene terephthalate, polybutylene terephthalate,polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, anacrylic resin, polyvinyl alcohol, polypropylene, an epoxy resin, and aphenol-resin. Further, a substrate in that a plastic film or sheet asdescribed above is placed on the surface of, for example, a substratemade of metal such as aluminum, copper, or iron, a substrate made ofceramic, or a substrate made of glass can also be used. Furthermore, asubstrate obtained by forming an SiO₂ oblique evaporation film on thesurface of the plastic film or sheet can also be used. The thickness ofa substrate is preferably 5 μm to 500 μm, more preferably 10 μm to 200μm, and most preferably 15 μm to 150 μm. Such thickness providessufficient strength for a substrate, and thus can prevent the generationof problems, for example, breaking upon manufacture.

Next, the spread layer is subjected to heat treatment to align theliquid crystal material in a state exhibiting a liquid crystal phase.The spread layer contains a chiral agent together with the liquidcrystal material, and thus the liquid crystal material provided withtorsion in a state exhibiting a liquid crystal phase is aligned. As aresult, the spread layer (liquid crystal material forming the spreadlayer) forms the cholesteric structure (helical structure).

The temperature conditions for the heat treatment may appropriately beset in accordance with the type of liquid crystal material(specifically, temperature at which the liquid crystal material exhibitsliquid crystallinity). To be more specific, the heating temperature ispreferably 40 to 120° C., more preferably 50 to 100° C., and mostpreferably 60 to 90° C. A heating temperature of 40° C. or highergenerally allows sufficient alignment of the liquid crystal material. Aheating temperature of 120° C. or lower expands selection of thesubstrate in consideration of heat resistance, for example, and thusallows selection of an optimal substrate in accordance with the liquidcrystal material. Further, a heating time is preferably 30 seconds ormore, more preferably 1 minute or more, particularly preferably 2minutes or more, and most preferably 4 minutes or more. In the casewhere a treatment time is less than 30 seconds, the liquid crystalmaterial may not sufficiently exhibit a liquid crystal state. Further,the heating time is preferably 10 minutes or less, more preferably 8minutes or less, and most preferably 7 minutes or less. In the casewhere the treatment time is more than 10 minutes, the additives may besublimed.

Next, the spread layer containing the liquid crystal material exhibitinga cholesteric structure is subjected to at least one of polymerizationtreatment and crosslinking treatment to fix the alignment (cholestericstructure) of the liquid crystal material. To be more specific, thepolymerization treatment is performed, to thereby polymerize the liquidcrystal material (polymerizable monomer) and/or chiral agent(polymerizable chiral agent) and fix the polymerizable monomer and/orpolymerizable chiral agent as a repeating unit of polymer molecules.Further, the crosslinking treatment is preformed, to thereby form athree-dimensional network structure of the liquid crystal material(crosslinking monomer) and/or chiral agent and fix the crosslinkingmonomer and/or chiral agent as apart of a crosslinked structure. As aresult, an alignment state of the liquid crystal material is fixed. Notethat the polymer or three-dimensional network structure to be formedthrough polymerization or crosslinking of the liquid crystal material is“non-liquid crystalline”. The thus-formed third optical compensationlayer does not transfer into a liquid crystal phase, glass phase, orcrystal phase due to temperature change unique to a liquid crystalcompound, for example, and no alignment change due to temperatureoccurs. As a result, the thus-formed third optical compensation layermay be used as a high performance optical compensation layer notaffected by the temperature change. The third optical compensation layerhas a selective reflection wavelength region optimized within a range of100 nm to 320 nm, and thus can significantly suppress light leak and thelike.

A specific procedure for the polymerization treatment or crosslinkingtreatment may appropriately be selected in accordance with the type ofpolymerization initiator or crosslinking agent to be used. For example,a photo-polymerization initiator or photo-crosslinking agent may be usedfor photoirradiation. A UV polymerization initiator or UV crosslinkingagent may be used for UV irradiation, and heat polymerization initiatoror heat crosslinking agent may be used for heating. The irradiation timeof light or UV light, the irradiation intensity, the total irradiationamount, and the like may appropriately be set in accordance with thetype of liquid crystal material, the type of substrate, propertiesdesired for the third optical compensation layer, and the like.Similarly, the heating temperature, the heating time, and the like mayappropriately be set in accordance with the purpose.

The cholesteric alignment fixed layer formed on the substrate asdescribed above is transferred onto a surface of the second opticalcompensation layer to form the third optical compensation layer. In thecase where the third optical compensation layer has a laminate structureof the cholesteric alignment fixed layer and the plastic film layer, theplastic film layer may be attached to the second optical compensationlayer-through a pressure-sensitive adhesive layer and the cholestericalignment fixed layer may be transferred to the plastic layer, tothereby form the third optical compensation layer. Alternatively, theplastic film layer may be attached to the cholesteric alignment fixedlayer formed on the substrate through an adhesive layer to form alaminate, and the laminate may be attached to the surface of the secondoptical compensation layer through a pressure-sensitive adhesive layer.The transfer step further includes peeling the substrate from the thirdoptical compensation layer. The curable adhesive for the adhesive layeris as described in the above section A-3. The plastic film layer is asdescribed in the above section A-4.

The above-mentioned typical example of the method of forming the thirdoptical compensation layer employs a liquid crystal monomer(polymerizable monomer or crosslinking monomer, for example) as theliquid crystal material, but the method of forming the third opticalcompensation layer of the present invention is not limited to such amethod and may be a method which employs a liquid crystalline polymer.However, the method preferably employs a liquid crystal monomer asdescribed above. The liquid crystal monomer may be used, to thereby forman optical compensation layer having an excellent optical compensationfunction and reduced thickness. To be specific, use of the liquidcrystal monomer facilitates control of the selective reflectionwavelength region. Further, the viscosity of the application liquid andthe like may easily be set by using the liquid crystal monomer, tothereby facilitate formation of a extremely thin third opticalcompensation layer. Further, the liquid crystal monomer has excellenthandling property. In addition, the optical compensation layer to beobtained has even better surface smoothness.

A-5. Polarizer

Any suitable polarizers may be employed as the polarizer 11 inaccordance with the purpose. Examples thereof include: a film preparedby adsorbing a dichromatic substance such as iodine or a dichromatic dyeon a hydrophilic polymer film such as a polyvinyl alcohol-based film, apartially formalized polyvinyl alcohol-based film, or a partiallysaponified ethylene/vinyl acetate copolymer-based film and uniaxiallystretching the film; and a polyene-based orientation film such as adehydrated product of a polyvinyl alcohol-based film or a dechlorinatedproduct of a polyvinyl chloride-based film. Of those, a polarizerprepared by adsorbing a dichromatic substance such as iodine on apolyvinyl alcohol-based film and uniaxially stretching the film isparticularly preferred because of high polarized dichromaticity. Athickness of the polarizer is not particularly limited, but is generallyabout 1 to 80 μm.

The polarizer prepared by adsorbing iodine on a polyvinyl alcohol-basedfilm and uniaxially stretching the film may be produced by, for example:immersing a polyvinyl alcohol-based film in an aqueous solution ofiodine for coloring; and stretching the film to a 3 to 7 times length ofthe original length. The aqueous solution may contain boric acid, zincsulfate, zinc chloride, or the like as required, or the polyvinylalcohol-based film may be immersed in an aqueous solution of potassiumiodide or the like. Further, the polyvinyl alcohol-based film may beimmersed and washed in water before coloring as required.

Washing the polyvinyl alcohol-based film with water not only allowsremoval of contamination or an antiblocking agent on a film surface, butalso provides an effect of preventing nonuniformity such as unevencoloring by swelling of the polyvinyl alcohol-based film. The stretchingof the film may be performed after coloring of the film with iodine,performed during coloring of the film, or performed followed by coloringof the film with iodine. The stretching may be performed in an aqueoussolution of boric acid or potassium iodide, or in a water bath.

A-6. Protective Film

Any suitable protective film which can be used as a protective layer fora polarizer may be employed as the protective film. Specific examples ofa material used as a main component of the film include transparentresins such as a cellulose-based resin (such as triacetylcellulose(TAC)), a polyester-based resin, a polyvinyl alcohol-based resin, apolycarbonate-based resin, a polyamide-based resin, a polyimide-basedresin, a polyether sulfone-based resin, a polysulfone-based resin, apolystyrene-based resin, a polynorbornene-based resin, apolyolefin-based resin, an acrylic resin, and an acetate-based resin.Another example thereof includes an acrylic, urethane-based, acrylicurethane-based, epoxy-based, or silicone-based thermosetting resin orUV-curing resin. Still another example thereof includes a glassy polymersuch as a siloxane-based polymer. Further, a polymer film described inJP2001-343529A (WO 01/37007) may also be used. More specifically, thefilm in the publication is formed of a resin composition containing athermoplastic resin having a substituted or unsubstituted imide group ona side chain, and a thermoplastic resin having a substituted orunsubstituted phenyl group and a nitrile group on a side chain. Aspecific example thereof includes a resin composition containing analternate copolymer of isobutene and N-methylmaleimide, and anacrylonitrile/styrene copolymer. The polymer film may be an extrudedproduct of the above-mentioned resin composition, for example. Of those,TAC, a polyimide-based resin, a polyvinyl alcohol-based resin and aglassy polymer are preferred. TAC is especially preferred.

It is preferred that the protective film be transparent and have nocolor. More specifically, the protective film has a thickness directionretardation of preferably −90 nm to +90 nm, more preferably −80 nm to+80 nm, and most preferably −70 nm to +70 nm.

The protective film has any suitable thickness as long as the preferredthickness direction retardation can be obtained. More specifically, thethickness of the protective film is preferably 5 mm or less, morepreferably 1 mm or less, especially preferably 1 to 500 μm, and mostpreferably 5 to 150 μm.

The surface of the protective film arranged at the outer side of thepolarizer 11 (that is, the opposite side with respect to the opticalcompensation layers) may be subjected to hard coat treatment,antireflection treatment, anti-sticking treatment, anti-glare treatment,or the like as required.

A-7. Other Components of Polarizing Plate Provided With OpticalCompensation Layers

The polarizing plate provided with optical compensation layers of thepresent invention may further include another optical layer. Anysuitable optical layers may be employed as the other optical layer inaccordance with the purpose or the type of image display. Specificexamples of the other optical layer include a liquid crystal film, alight scattering film, a diffraction film and other optical compensationlayer (retardation film).

The polarizing plate provided with optical compensation layers of thepresent invention may further include a sticking layer as an outermostlayer on at least one side. Inclusion of the sticking layer as anoutermost layer facilitates lamination of the polarizing plate withother members (such as liquid crystal cell), to thereby prevent peelingoff of the polarizing plate from other members. Any suitable materialsmay be employed as a material for the sticking layer. Specific examplesof the material include the pressure sensitive adhesive described in thesection A-2, and the adhesive described in the section A-3. A materialhaving excellent humidity resistance and thermal resistance ispreferably used in view of preventing foaming or peeling due to moistureabsorption, degradation of optical characteristics and warping of aliquid crystal cell due to difference in thermal expansion, and thelike.

For practical purposes, the surface of the sticking layer is coveredwith an appropriate separator until the polarizing plate is actuallyused, to thereby prevent contamination. The separator may be formed byproviding a release coating on any suitable film by using asilicone-based, long-chain alkyl-based, fluorine-based, or molybdenumsulfide release agent, for example.

Each layer of the polarizing plate provided with optical compensationlayers of the present invention may be provided with UV absorbabilitythrough treatment with a UV absorber such as a salicylate-basedcompound, a benzophenone-based compound, a benzotriazole-based compound,a cyanoacrylate-based compound, or a nickel complex salt-based compound.

B. Method of Producing Polarizing Plate

The polarizing plate provided with optical compensation layers of thepresent invention may be produced by laminating the above-mentionedlayers through the above-mentioned adhesive layer or pressure-sensitiveadhesive layer. Any appropriate laminating, method may be employed aslong as the optical axes of the respective layers form angles (angles α,β, and γ) within the above ranges. For example, the polarizer, the firstoptical compensation layer, the second optical compensation layer, andthe third optical compensation layer may be punched out intopredetermined sizes, aligned so as to form the angles α, β, and γdescribed above, and laminated through an adhesive or apressure-sensitive adhesive.

C. Use of Polarizing Plate

The polarizing plate provided with optical compensation layers of thepresent invention may be suitably used for various image displays (suchas liquid crystal display and selfluminous display). Specific examplesof the image display for which the polarizing plate provided withoptical compensation layers may be used include a liquid crystaldisplay, an EL display, a plasma display (PD), and a field emissiondisplay (FED). The polarizing plate provided with optical compensationlayers of the present invention used for a liquid crystal display isuseful for viewing angle compensation, for example. The polarizing plateprovided with optical compensation layers of the present invention isused for a liquid crystal display of a circularly polarization mode, andis particularly useful for a homogeneous alignment TN liquid crystaldisplay, an in-plane switching (IPS) liquid crystal display, and avertical alignment (VA) liquid crystal display. The polarizing plateprovided with optical compensation layers of the present invention usedfor an EL display is useful for prevention of electrode reflection, forexample.

D. Image Display Apparatus

A liquid crystal display apparatus is described as an example of theimage display apparatus of the present invention. A liquid crystal panelto be used for the liquid crystal display apparatus is described. Otherstructure of the liquid crystal display apparatus may employ anyappropriate structure in accordance with the purpose. In the presentinvention, a liquid crystal display apparatus of VA mode is preferred,and a liquid crystal display apparatus of reflective orsemi-transmissive VA mode is particularly preferred. FIG. 3 is aschematic sectional view of a liquid crystal panel according to apreferred embodiment of the present invention. A liquid crystal panelfor a reflective liquid crystal display apparatus is described withreference to FIG. 3. A liquid crystal panel 100 is provided with: aliquid crystal cell 20; a retardation plate 30 arranged on an upper sideof the liquid crystal cell 20; and a polarizing plate 10 arranged on anupper side of the retardation plate 30. The retardation plate 30 mayemploy any appropriate retardation plate in accordance with the purposeand the alignment mode of the liquid crystal cell. The retardation plate30 may be omitted in accordance with the purpose and the alignment modeof the liquid crystal cell. The polarizing plate 10 refers to thepolarizing plate provided with optical compensation layers of thepresent invention described in the above sections A and B. The liquidcrystal cell 20 includes: a pair of glass substrates 21 and 21′; and aliquid crystal layer 22 as a display medium arranged between thesubstrates. A reflecting electrode 23 is provided on a liquid crystallayer side of the lower substrate 21′, and color filters (not shown) areprovided on the upper substrate 21. A distance (cell gap) between thesubstrates 21 and 21′ is controlled by a spacer 24.

In the liquid crystal display apparatus 100 of reflective VA mode, forexample, liquid crystal molecules are aligned vertically to surfaces ofthe substrates 21 and 21′ under no voltage application. Such verticalalignment may be realized by arranging nematic liquid crystals havingnegative dielectric anisotropy between substrates each having formedthereon a vertically aligned film (not shown). Linear polarized lightallowed to pass through the polarizing plate 10 from a surface of theupper substrate 21 entering the liquid crystal layer 22 in such a stateadvances along long axes of vertically aligned liquid crystal molecules.No birefringence generates in a long axis direction of the liquidcrystal molecules such that incident light advances without changing apolarization direction. The light is reflected by the reflectingelectrode 23, is allowed to pass through the liquid crystal cell 22, andexits from the upper substrate 21. A polarization state of the exitinglight is the same as that of the incident light, and the exiting lightis allowed to pass through the polarizing plate 10, to thereby providelight display. Long axes of the liquid crystal molecules align parallelto the surfaces of the substrates under voltage application betweenelectrodes. The liquid crystal molecules exhibit birefringence withrespect to linear polarized light entering the liquid crystal layer 22in such a state, and the polarization state of incident light variesdepending on inclination of the liquid crystal molecules. Lightreflected by the reflecting electrode 23 and exiting from the uppersubstrate under application of a predetermined maximum voltage rotatesits polarization direction by 90° into linear polarized light, forexample, and is absorbed by the polarizing plate 10, to thereby providedark display. Return to a state under no voltage application provideslight display again by alignment control force. The inclination of theliquid crystal molecules may be controlled by varying an applicationvoltage to change an intensity of transmitted light from the polarizingplate 10, to thereby provide gradation display.

Hereinafter, the present invention is described more specifically by wayof examples. However, the present invention is not limited to theexamples. Methods of measuring properties in examples are describedbelow.

(1) Measurement of Thickness

The thickness of each of the polarizing plates provided with opticalcompensation layers of Examples and Comparative Examples was measured byusing Dial Gauge manufactured by Ozaki Mfg. Co., Ltd.

(2) Measurement of Uneven Display Due to Heat

Each of the polarizing plates provided with optical compensation layersobtained in Examples and Comparative Examples was attached to the samepolarizing plate provided with optical compensation layers, to therebyprepare a measurement sample. The polarizing plates provided withoptical compensation layers were attached together such that absorptionaxes of the respective polarizers were perpendicular to each other andthat the respective third optical compensation layers opposed eachother. This measurement sample was placed on backlight, and an imageilluminated with backlight was photographed with a digital camera. Thephotographed image was grayed (256 gradation) by using Win Roof v3.0manufactured by Mitani Corporation. The 35th gradation level of 0 to 255brightness gradation levels was used as a threshold, and the gradationlevels was binarized into 0 to 35 gradation levels as white and 35 to255 gradation levels as black. A ratio of white in the image wasrepresented by %. The measurement sample was heated at 85° C. for 10minutes, and the ratio of white before and after heating was measured.The change in the ratio of white was determined, and a small changeindicated little uneven display due to heat.

(3) Measurement of Transmittance

Each of the polarizing plates provided with optical compensation layersobtained in Examples and Comparative Examples was attached to the samepolarizing plate provided with optical compensation layers, to therebyprepare a measurement sample. The polarizing plates provided withoptical compensation layers were attached together such that absorptionaxes of the respective polarizers were perpendicular to each other andthat the respective third optical compensation layers opposed eachother. The transmittance of the measurement sample was measured by usingDOT-3, trade name, manufactured by Murakami Color Research Laboratory.

EXAMPLE 1

(Production of Polarizer)

A commercially available polyvinyl alcohol (PVA) film (available fromKuraray Co., Ltd.) was colored in an aqueous solution containing iodineand uniaxially stretched to about a 6 times length between rolls havingdifferent speed ratios in an aqueous solution containing boric acid, tothereby obtain a continuous polarizer. A commercially available TAC film(available from Fuji Photo Film Co., Ltd.) was attached to each side ofthe polarizer by using a PVA-based adhesive, to thereby obtain apolarizing plate (protective film/polarizer/protective film) having atotal thickness of 100 μm. This polarizing plate was punched out intolength of 20 cm and width of 30 cm such that an absorption axis of thepolarizer was set in a longitudinal direction.

(Production of First Optical Compensation Layer)

A continuous norbornene-based resin film (trade name, Zeonoa, availablefrom Zeon Corporation, thickness of 60 μm, photoelastic coefficient of3.10×10⁻¹² m²/N) was uniaxially stretched to a 1.90 times length at 140°C., to thereby produce a continuous film for a first opticalcompensation layer. This film had a thickness of 45 μm and an in-planeretardation Re₁ of 270 nm. This film was punched out into length of 20cm and width of 30 cm such that its slow axis was set in a longitudinaldirection.

(Production of Second Optical Compensation Layer)

A continuous norbornene-based resin film (trade name, Zeonoa, availablefrom Zeon Corporation, thickness of 60 μm, photoelastic coefficient of3.10×10⁻¹² m²/N) was uniaxially stretched to a 1.32 times length at 140°C., to thereby produce a continuous film for a second opticalcompensation layer. This film had a thickness of 50 μm and an in-planeretardation Re₂ of 140 nm. This film was punched out into length of 20cm and width of 30 cm such that its slow axis was set in a longitudinaldirection.

(Production of Third Optical Compensation Layer)

90 parts by weight of a nematic liquid crystal compound represented bythe following formula (10), 10 parts by weight of a chiral agentrepresented by the following formula (38), 5 parts by weight of aphoto-polymerization initiator (Irgacure 907, available from CibaSpecialty Chemicals), and 300 parts by weight of methyl ethyl ketonewere mixed uniformly, to thereby prepare a liquid crystal applicationliquid. This liquid crystal application liquid was used to coat asubstrate (biaxially stretched PET film), subjected to heat treatment at80° C. for 3 minutes, and subjected to polymerization treatment byirradiating the liquid crystal application liquid with UV light, tothereby form a third optical compensation layer. The substrate havingthe third optical compensation layer formed thereon was punched out intolength of 20 cm×width of 30 cm. The third optical compensation layer hada thickness of 2 μm, an in-plane retardation Re₃ of 0 nm, and athickness direction retardation Rth₃ of 110 nm.

(Production of Polarizing Plate Provided With Optical CompensationLayers)

The polarizing plate, first optical compensation layer, second opticalcompensation layer, and third optical compensation layer obtained abovewere laminated in the stated order. The lamination was performed suchthat the slow axes of the first optical compensation layer, secondoptical compensation layer, and third optical compensation layer were at15°, 75°, and 75°, respectively, in a counterclockwise direction withrespect to the absorption axis of the polarizer of the polarizing plate.The polarizer and the first optical compensation layer, and the firstoptical compensation layer and the second optical compensation layerwere laminated by using an acrylic pressure-sensitive adhesive(thickness of 20 μm). The second optical compensation layer and thethird optical compensation layer were laminated by using anisocyanate-based curable adhesive (thickness of 5 μm). Next, thesubstrate (biaxially stretched PET film) supporting the third opticalcompensation layer was peeled off, and an acrylic pressure-sensitiveadhesive (thickness of 20 μm) was applied to the peeled surface forattaching the liquid crystal cell thereto. Finally, the resultant waspunched out into length of 4.0 cm and width of 5.3 cm, to thereby obtaina polarizing plate provided with optical compensation layers as shown inFIG. 1.

The obtained polarizing plate provided with optical compensation layerswas measured for thickness, transmittance, and uneven display due toheat. Table 1 shows the results together with the results of Examples 2and 3 and Comparative Examples 1 to 3 described below. TABLE 1 Unevendisplay due to heat Before After Change Thickness Transmittance heatingheating amount (μm) (%) (%) (%) (%) Example 1 262 0.10 0.21 1.55 1.34Example 2 340 0.10 7.53 12.18 4.65 Example 3 322 0.10 0.25 1.60 1.35Comparative 262 0.85 1.22 2.60 1.38 example 1 Comparative 262 0.80 1.282.70 1.42 example 2 Comparative 340 0.85 8.02 12.54 4.52 example 3

EXAMPLE 2

The polarizing plate, the first optical compensation layer, and thesecond optical compensation layer were produced in the same manner as inExample 1.

(Production of Third Optical Compensation Layer)

A continuous norbornene-based film (trade name, Arton, available fromJSR Corporation, thickness of 100 μm, photoelastic coefficient of5.00×10⁻¹² m²/N) was longitudinally stretched to an about 1.27 timeslength at 175° C. and then transversely stretched to an about 1.37 timeslength at 176° C., to thereby produce a continuous film (thickness of 65μm) for a third optical compensation layer. This film was punched outinto length of 20 cm and width of 30 cm, to thereby form a third opticalcompensation layer. The third optical compensation layer had an in-planeretardation Re₃ of 0 nm and a thickness direction retardation Rth₃ of110 nm.

(Production of Polarizing Plate Provided With Optical CompensationLayers)

A polarizing plate provided with optical compensation layers as shown inFIG. 1 was produced in the same manner as in Example 1 except that thesecond optical compensation layer and the third optical compensationlayer were laminated by using an acrylic pressure-sensitive adhesive(thickness of 20 μm). The obtained polarizing plate provided withoptical compensation layers was subjected to the same evaluation as thatof Example 1. Table 1 shows the results.

EXAMPLE 3

The polarizing plate, the first optical compensation layer, and thesecond optical compensation layer were produced in the same manner as inExample 1.

The liquid crystal application liquid prepared in the same manner as inExample 1 was used to coat a substrate (biaxially stretched PET film),subjected to heat treatment at 80° C. for 3 minutes, and subjected topolymerization treatment by irradiating the liquid crystal applicationliquid with UV light, to thereby form a cholesteric alignment fixedlayer (thickness of 2 μm). Next, an isocyanate-based curable adhesive(thickness of 5 μm) was applied to the cholesteric alignment fixedlayer, and a plastic film layer (TAC film, thickness of 40 μm) wasattached thereto through the adhesive, to thereby form a third opticalcompensation layer. The third optical compensation layer was punched outinto length of 20 cm and width of 30 cm. The third optical compensationlayer had a thickness of 47 μm, an in-plane retardation Re₃ of 0 nm, anda thickness direction retardation Rth₃ of 140 nm.

The polarizer, the first optical compensation layer, the second opticalcompensation layer, and the third optical compensation layer werelaminated in the stated order in the same manner as in Example 1, tothereby obtain a polarizing plate provided with optical compensationlayers as shown in FIG. 1 except that the second optical compensationlayer and the third optical compensation layer were laminated through anacrylic pressure-sensitive adhesive (thickness of 20 μm). At this time,the second optical compensation layer and the third optical compensationlayer were laminated such that the plastic film layer (TAC film) of thethird optical compensation layer opposed the second optical compensationlayer. The obtained polarizing plate provided with optical compensationlayers was subjected to the same evaluation as that of Example 1. Table1 shows the results.

COMPARATIVE EXAMPLE 1

A polarizing plate provided with optical compensation layers wasproduced in the same manner as in Example 1 except that the slow axis ofthe first optical compensation layer was at 35° in a counterclockwisedirection with respect to the absorption axis of the polarizer of thepolarizing plate. The obtained polarizing plate provided with opticalcompensation layers was subjected to the same evaluation as that ofExample 1. Table 1 shows the results.

COMPARATIVE EXAMPLE 2

A polarizing plate provided with optical compensation layers wasproduced in the same manner as in Example 1 except that the slow axis ofthe second optical compensation layer was at 35° in a counterclockwisedirection with respect to the absorption axis of the polarizer of thepolarizing plate. The obtained polarizing plate provided with opticalcompensation layers was subjected to the same evaluation as that ofExample 1. Table 1 shows the results.

COMPARATIVE EXAMPLE 3

A polarizing plate provided with optical compensation layers wasproduced in the same manner as in Example 2 except that the slow axis ofthe first optical compensation layer was at 35° in a counterclockwisedirection with respect to the absorption axis of the polarizer of thepolarizing plate. The obtained polarizing plate provided with opticalcompensation layers was subjected to the same evaluation as that ofExample 1. Table 1 shows the results.

Table 1 revealed the following. In Examples of the present invention,angles between the slow axes of the first optical compensation layer,second optical compensation layer, and third optical compensation layer,and the absorption axis of the polarizer were set within a predeterminedrange, and thus transmittance in a crossed nicols state was greatlyreduced. That is, light leak in black display was favorably prevented.Meanwhile, in Comparative Examples, at least one angle formed betweenthe slow axes of the optical compensation layers and the absorption axisof the polarizer depart from the predetermined range, and thus thetransmittance in a crossed nicols state was very large. That is, lightleak in black display was extremely significant and not at practicallevel. Further, in Comparative Examples, at least one angle formedbetween the slow axes of the optical compensation layers and theabsorption axis of the polarizer depart from the predetermined range,and a high value was obtained from an initial value in the test ofuneven display due to heat. A comparison between Examples 1 and 3, andExample 2 reveals that the cholesteric alignment fixed layer is employedas the third optical compensation layer, to thereby prevent both lightleak and uneven display due to heat. Further, use of theisocyanate-based curable adhesive for lamination of the third opticalcompensation layer actually confirmed favorable prevention of formationof cracks in the third optical compensation layer during heating.

INDUSTRIAL APPLICABILITY

The polarizing plate provided with optical compensation layers of thepresent invention may suitably be used for various image displayapparatuses (such as a liquid crystal display apparatus and aself-luminous display apparatus).

1. A polarizing plate provided with optical compensation layerscomprising a polarizer, a first optical compensation layer, a secondoptical compensation layer, and a third optical compensation layer inthe stated order, wherein: the first optical compensation layer containsa resin having an absolute value of photoelastic coefficient of 2×10⁻¹¹m²/N or less, and has a relationship of nx>ny=nz and an in-planeretardation Re₁ of 200 to 300 nm; the second optical compensation layercontains a resin having an absolute value of photoelastic coefficient of2×10⁻¹¹ m²/N or less, and has a relationship of nx>ny=nz and an in-planeretardation Re₂ of 90 to 160 nm; the third optical compensation layerhas a relationship of nx=ny>nz, an in-plane retardation Re₃ of 0 to 20nm, and a thickness direction retardation Rth₃ of 30 to 300 nm; anabsorption axis of the polarizer and a slow axis of the first opticalcompensation layer form an angle of 10° to 30°; the absorption axis ofthe polarizer and a slow axis of the second optical compensation layerform an angle of 70° to 95°; and the absorption axis of the polarizerand a slow axis of the third optical compensation layer form an angle of70° to 95°.
 2. A polarizing plate provided with optical compensationlayers according to claim 1, wherein the third optical compensationlayer has a thickness of 1 to 50 μm.
 3. A polarizing plate provided withoptical compensation layers according to claim 1, wherein the thirdoptical compensation layer is formed of a cholesteric alignment fixedlayer having a selective reflection wavelength region of 350 nm or less.4. A polarizing plate provided with optical compensation layersaccording to claim 1, wherein the third optical compensation layerincludes a layer formed of a film having a relationship of nx=ny>nz andcontaining a resin having an absolute value of photoelastic coefficientof 2×10⁻¹¹ m²/N or less and a cholesteric alignment fixed layer having aselective reflection wavelength region of 350 nm or less.
 5. A liquidcrystal panel comprising the polarizing plate provided with opticalcompensation layers according to claim 1, and a liquid crystal cell. 6.A liquid crystal panel according to claim 5, wherein the liquid crystalcell is of reflective or semi-transmissive VA mode.
 7. A liquid crystaldisplay apparatus comprising the liquid crystal panel according to claim5.
 8. An image display apparatus comprising the polarizing plateprovided with optical compensation layers according to claim
 1. 9. Apolarizing plate provided with optical compensation layers according toclaim 2, wherein the third optical compensation layer is formed of acholesteric alignment fixed layer having a selective reflectionwavelength region of 350 nm or less.
 10. A polarizing plate providedwith optical compensation layers according to claim 2, wherein the thirdoptical compensation layer includes a layer formed of a film having arelationship of nx=ny>nz and containing a resin having an absolute valueof photoelastic coefficient of 2×10⁻¹¹ m²/N or less and a cholestericalignment fixed layer having a selective reflection wavelength region of350 nm or less.
 11. A liquid crystal panel comprising the polarizingplate provided with optical compensation layers according to claim 2,and a liquid crystal cell.
 12. A liquid crystal panel comprising thepolarizing plate provided with optical compensation layers according toclaim 3, and a liquid crystal cell.
 13. A liquid crystal panelcomprising the polarizing plate provided with optical compensationlayers according to claim 4, and a liquid crystal cell.
 14. A liquidcrystal panel according to claim 11, wherein the liquid crystal cell isof reflective or semi-transmissive VA mode.
 15. A liquid crystal panelaccording to claim 12, wherein the liquid crystal cell is of reflectiveor semi-transmissive VA mode.
 16. A liquid crystal panel according toclaim 13, wherein the liquid crystal cell is of reflective orsemi-transmissive VA mode.
 17. A liquid crystal display apparatuscomprising the liquid crystal panel according to claim
 6. 18. An imagedisplay apparatus comprising the polarizing plate provided with opticalcompensation layers according to claim
 2. 19. An image display apparatuscomprising the polarizing plate provided with optical compensationlayers according to claim
 3. 20. An image display apparatus comprisingthe polarizing plate provided with optical compensation layers accordingto claim 4.